With wet conditions making it a challenge to put up hay at desired moisture levels in many parts of the country, hay growers will want to be especially alert for signs of bale heating, says Marc Sulc, forage specialist with Ohio State University Extension.
"Every year someone's barn burns down because of spontaneous combustion of wet hay," says Sulc. "So if you have hay that is on the wet side, keep it outside or in a well-ventilated area. Don't stack wet hay, either, because that prevents the heat and moisture left in the hay from escaping."
If you do happen to bale at higher moisture contents than desired, he advises keeping a close watch on the hay for two to three weeks. "You should invest in a hay temperature probe and monitor the internal temperature of the hay during the first three weeks."
Sulc notes that it's normal for hay to go through a "sweat" in the first few days after baling. Internal temperatures of 110 degrees F in the first five days after baling are quite common in the eastern Corn Belt and are not a concern. Hay-bale temperatures of 120-130 degrees will likely result in mold growth and will make the protein in the hay less available to animals. But at those temperatures, there still is not a danger of fire.
The concern is if mold growth causes the temperature to go even higher, he says. "If the temperature in the hay continues to rise, reaching 160-170 degrees, then there is cause for alarm. At those elevated temperatures, other chemical reactions begin to occur that elevate the temperature much higher, resulting in spontaneous combustion of the hay in a relatively short period of time."